title: Free immunoglobulin light chain: its biology and implications in diseases.
abstract: Immunoglobulin light chain (IgLC) is a component of antibodies, but its free form is observed in the circulation, which originates from 10 to 40% excess synthesis over heavy chain in B cells. Complete antibodies function as a defined tetramer structure unit, H2L2; thus, separation of heavy and light chains results in considerable or complete loss of antigen-binding ability. Free IgLC has been considered as an inconsequential spillover during antibody assembly because, unlike heavy chain, neither effector functions such as complement activation nor specific-receptor binding has been identified in IgLCs. Free IgLC in sera and cerebrospinal fluids increases in inflammatory diseases such as autoimmune diseases and infections, presumably as a result of B-cell activation. This may be just a concomitant event during elevated disease activity, but recent findings suggest that free IgLC is involved in a wide range of immunological phenomena as a signaling effector or an anti-inflammatory molecule. These effects are likely to be intrinsic to IgLC. In this review, we attempt to give a comprehensive view about the biological roles of free IgLC together with the gene expression, secretion, antigen-binding ability, and its metabolic characteristics.
authors.affiliation: Department of Biochemistry, Faculty of Medicine, Saitama Medical University, Saitama, Japan. nk.takanari@gmail.com
authors.forename: Takanari
authors.initials: T
authors.lastname: Nakano
authors.forename: Masanori
authors.initials: M
authors.lastname: Matsui
authors.forename: Ikuo
authors.initials: I
authors.lastname: Inoue
authors.forename: Takuya
authors.initials: T
authors.lastname: Awata
authors.forename: Shigehiro
authors.initials: S
authors.lastname: Katayama
authors.forename: Takayuki
authors.initials: T
authors.lastname: Murakoshi
mesh_terms: D000818:Animals; D000941:Antigens / Q000276:immunology; D004194:Disease; D005786:Gene Expression Regulation; D006801:Humans; D007147:Immunoglobulin Light Chains / Q000096:biosynthesis / Q000276:immunology / Q000378:metabolism*
chemical_list: D000941:Antigens; D007147:Immunoglobulin Light Chains